The present invention relates to a high-speed pouch forming, filling and sealing machine and method of operation using a multi-layer film structure that can be used for packaging consumable liquid products, such as flowable dairy products, fluid milk, sour cream, yoghurt, fruit juices, water, in flexible plastic pouches.
Traditionally, in North America, the film used for packaging fluid milk or the like in flexible plastic pouches consists of a 76 microns (3 mil) mono-layer polyethylene film.
However, this standard film has some disadvantages which should be overcome. For example, the packaging operation requires a certain amount of electrical energy for the heat sealing operation due to the thickness of the film. To generate this heat, electrical energy is dispensed. It is desirable to develop a process that could generate the energy consumption in order to make the operation more economically feasible. Another problem involved with the sealing operation is that some of the hardware, such as the sealing element per se and the rubber and Teflon(trademark) parts associated with the sealing jaws have a relatively short useful life, requiring frequent changes and again increasing the cost of producing milk pouches.
Yet another problem resulting from the packaging of liquids with a mono-layer polyethylene film is the amount of waste and machine downtime due to film roll changes and seal breaks. Packaging milk or other liquids with mono-layer polyethylene also involves the use of a narrow sealing window which renders the operation somewhat difficult. Finally, the seals obtained with this type of film pouches, often exhibits weaknesses that can cause fluid leakage.
Polymer film pouches made from a polyethylene film structure and used for packaging flowable materials such as milk, are known and examples of such are described in U.S. Pat. Nos. 5,288,531; 5,360,648; 5,364,486 and 5,508,051, all of which have issued to the Dow Chemical Company.
U.S. Pat. No. 5,972,443 discloses a multi-layer film comprising a layer of high density polyethylene (HDPE) as the stiffening layer, and a layer of copolymer of ethylene/C4-C10 xcex1-olefin, also referred to as a metallocene resin. An important disadvantage with HDPE is that although it has a high density, by the industry standards, its rigidity is such that a great amount thereof must be used to reach an acceptable level.
U.S. Pat. No. 5,849,127 describes a multi-layer film comprising at least 3 layers, i.e., a first layer made of a metallocene resin (or ethylene/xcex1-olefin copolymer); a second layer made of a polyolefin; and a third layer made of a second metallocene resin, the second layer being chemically different from the first and third layer, and sandwiched therebetween.
WO 9414609 describes a multi-layer coextruded film comprising two outer layers of a metallocene resin (referred to as linear low density polyethylene), and an intermediate layer of a blend of linear low density polyethylene and a polyolefin selected from the group consisting of homopolymers of propylene, copolymers of propylene and ethylene, and mixtures thereof.
It would therefore be highly desirable to develop a multi-layer film comprising a stiffening layer having improved properties. For example, if the material of the stiffening layer had a lower density combined with a higher rigidity, this would allow a higher yield than with HDPE for a given rigidity requirement.
It is a feature of the present invention to provide a thinner multi-layer coextruded film structure, which overcomes some or all of the disadvantages of the prior art and incorporated in a pouch forming, filling and sealing machine to improve on its method of operation and throughput.
It is another feature of the present invention to provide fluid containing pouches that exhibit desirable properties as compared to the pouches of the prior art. These pouches are made of a multi-layer film structure according to the invention that improves horizontal seal strength, exhibits lower horizontal seal thinning, and minimizes post consumer waste. The pouches therefore have a higher stiffness enabling pouring of liquid, and exhibit a substantial improvement in drop test performance and puncture resistance.
It is another feature of the invention to provide a multi-layer film structure which makes it possible to reduce the material used as compared to the films of the prior art, thereby providing a higher yield.
It is another feature of the present invention to provide a multi-layer film structure for packaging liquid that can be sealed at much lower seal initiation temperature and has greater machine direction tensile strength.
It is another feature of the present invention to provide a multi-layer film structure for packaging liquid into pouches, which ensures a reduction of the electrical energy required for sealing due to lower heat initiation temperature and lower mass to be sealed.
It is another feature of the present invention to provide a multi-layer film structure for packaging consumable liquid products into pouches which uses lower sealing temperature and thereby improves the useful life of the jaw sealers, such as the rubber, and electrical sealing heads, and resulting in overall energy reduction.
It is another feature of the present invention to provide a multi-layer film structure for packaging liquid wherein sealing is easier to operate due to a wider sealing window, and speed increase is made possible as a result of a faster sealing cycle.
According to another feature of the present invention there is provided a high-speed pouch forming, filling and sealing machine and its method of operation and utilizing sealing heads which operate at lower temperatures due to a decrease in the film thickness as compared with 76 microns (3 mil) mono-layer polyethylene film and thereby resulting in an electrical energy saving and wherein the thin film permits the machine to obtain a substantially higher yield with a film roll substantially the same size as with the 76 xcexcm (3 mil) film.
According to the above features, from a broad aspect, the present invention provides a multi-layer structure for use in packaging consumable liquid into flexible pouches comprising an inner sealing layer, an outer layer, and a core comprising one or more layers sandwiched between said sealing layer and said outer layer, wherein
the sealing layer comprises about 40% to 100% weight percent of a polyethylene/xcex1-olefin copolymer, also known as a metallocene resin, having a density of between about 0.902 and 0.912, and about 0 to 60 weight percent of a polyolefin, preferably low density polyethylene, or a mixture of at least 2 polyolefins, preferably low density polyethylene, linear low density polyethylene.
the outer layer comprises a polyolefin, preferably low density polyethylene, or a mixture of at least 2 polyolefins, preferably low density polyethylene, linear low density polyethylene or very low linear density polyethylene,
the core comprising at least one layer made of a mixture of about 20 to 90 weight percent of a polypropylene homopolymer, copolymer or terpolymer, and about 10 to 80 weight percent of a polyolefin, preferably low density polyethylene, or a mixture of at least 2 polyolefins, preferably low density polyethylene and linear low density polyethylene,
said multi-layer structure having a thickness within a range between about 50 and 70 xcexcm (2.0-2.75 mil).
The use of polypropylene homopolymer, copolymer or terpolymer in the core (or stiffening layer) is particularly advantageous for several reasons. It has a melting point higher than HDPE, thereby allowing a higher viscous strength during the sealing process because polypropylene solidifies at a higher temperature. It also has a rigidity significantly higher and a density lower than those of HDPE. As a result, because the density is lower, the yield is higher.
According to a still further broad aspect of the present invention there is provided a high-speed pouch forming, filling and sealing machine which comprises means to draw a multi-layer film from a film roll over a pouch-former to form a plastic film tube having an overlap vertical film edge. A vertical sealer is provided and has a sealing head for heat fusing the overlap vertical film edge form a vertical seal. A filler tube extends into the plastic film tube for injecting a consumable liquid product at a filling location of the plastic film tube. A horizontal sealing jaw, having an electrical thermal sealing element, is provided for effecting a horizontal seal across the plastic film tube and spaced below the filling location and for simultaneously severing the tube to form a top transverse seal for a filled pouch and a bottom transverse seal for a pouch being filled. The multi-layer film has an inner sealing layer, an outer layer and a core sandwiched therebetween. The characteristics of this film are described above. The horizontal and vertical seals have an improved seal strength of 30% to 50% as compared with the 76 xcexcm (3 mil) mono-layer polyethylene film and a 10xc2x0 C. to 15xc2x0 C. reduction in seal initiation temperature, an improved machine direction tensile strength of 25% to 40% and an improvement of 30% to 50% in puncture resistance, while reducing the sealing cycle time and increasing the throughput of the machine.
According to a still further broad aspect of the present invention there is provided a method of forming, filling and sealing a pouch with a consumable liquid at high-speed. The method comprises the steps of providing, in roll form, a multi-layer film sheet having an inner sealing layer, an outer layer and a core sandwiched therebetween, as described above. The film sheet is drawn, by drawing means over a pouch-former to form a plastic film tube having an overlap vertical film edge. The overlapped vertical film edge is sealed by a vertical sealer to form a vertical seal. A horizontal seal is formed across the plastic film tube by a horizontal sealing jaw positioned at a predetermined location below the vertical sealer. Simultaneously as the horizontal seal is made, the horizontal sealing jaw severs the tube and forms a top horizontal seal for a filled film pouch and a bottom horizontal seal for a pouch being formed and filled. The horizontal and vertical seals have an improved seal strength of 30% to 50% as compared with a 76 xcexcm (3 mil) mono-layer polyethylene film and a 10xc2x0 C. to 15xc2x0 C. reduction in seal initiation temperature and an improved machine direction tensile strength of 25 to 40%, while reducing the sealing cycle time. A consumable liquid is continuously fed within the plastic film tube below the vertical sealer and above the horizontal sealing jaw at a filling location.